1. Field of the Invention
The present invention relates to an antenna coupling module comprised of a planar antenna and a planar circuit type superconductive high frequency circuit and having the antenna and high frequency circuit electromagnetically coupled.
2. Description of the Related Art
As a planar circuit type antenna using a dielectric substrate, for example, one of a microstrip structure comprised of a pattern of dipole type, patch type, log-periodic, or other antenna elements formed on a substrate and having the opposite side of the substrate made a grounded surface may be mentioned, but various other patterns may also be considered. The input/output of high frequency electrical signals from the feeder point of the antenna elements is usually performed by the method of arranging a feeder line (transmission line) perpendicular to or on the same plane as the element plane. In the case of arrangement on the same plane, the method may be mentioned of forming the transmission line integrally with the antenna element pattern and arranging wirings with the transmission line to the input/output terminals on the substrate. Further, in the case of arrangement perpendicular to the element plane, the method maybe mentioned of arranging a feeder line passing through a through hole (via) so as to not directly contact the grounded surface at the opposite side of the substrate.
Further, when the impedance does not match with the feeder line or for balanced or unbalanced line transformation, there is the method of introducing a suitable matching circuit or balanced-to-unbalanced line transformer circuit, etc., between the feeder line and the antenna elements.
As a planar circuit type antenna, one using an oxide superconductor is being studied. With the microstrip structure, one forming a dipole type, patch type, log-periodic type, or other superconductive film pattern at one side of the dielectric substrate and forming a grounded surface by that superconductor or ordinary conductive metal at the opposite side of the substrate may be mentioned. Further, in a planar circuit type antenna using an oxide superconductor, the technique of forming a superconductor filter and a feeder point of antenna on the same dielectric substrate and transferring high frequency electrical signals between the filter and feeder point of the antenna is being studied. As a passive circuit using such an oxide superconductor, the technique of forming a film of a copper oxide high-temperature superconductor on a substrate and forming a high frequency filter or other circuit by a planar circuit (microstrip line type circuit, coplanar type circuit, etc.), may be mentioned (M. Hein, High-Temperature Superconductor Thin Films at Microwave Frequencies, Springer, 1999; Alan M. Portis, Electrodynamics of High-Temperature Superconductors, World Scientific, 1992; Zhi-Yuan She, High-Temperature Superconducting Microwave Circuits, Artech House, 1994; etc.) If selecting a suitable copper oxide high-temperature superconductor film material with excellent crystallinity, it is possible to obtain a lower surface resistance compared with the usual good electrical conductors of copper, silver, gold, aluminum, etc., at a quasi-microwave band, microwave band, etc. Therefore, it is known that use of this copper oxide high-temperature superconductive film material is advantageous for a low energy loss (hereinafter abbreviated as a “high Q-value”, reciprocal of dielectric loss tangent) and formation of a high Q-value circuit. To form a superconductive planar type circuit, a pattern of a film of an oxide high-temperature superconductor is formed in accordance with need on one or both surfaces of the dielectric substrate such as magnesium oxide or lanthanum aluminate. The superconductive film epitaxially grown on the substrate perpendicularly with respect to the crystal lattice c-axis is advantageous for the formation of a high Q-value circuit. A YBCO superconductive film, etc., is used as the superconductive film.
Further, while there are problems in practical use, by making the operating temperature one near the temperature of liquid helium (LHe) (4.2K), a circuit using a superconductive film theoretically can be made a superior one using a usual good electrical conductor even for the milliwave band or more (0.3 THz or more).
An antenna coupling module comprising a combination of a planar antenna and a planar circuit type superconductive high frequency circuit is, for example, disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-95213 (in particular, the claims and FIGS. 1 and 5). This publication discloses an oxide superconductive antenna module comprised of a feeder system, matching circuit, and radiation element wherein the radiation element is formed by a meandering single line comprised of an oxide superconductive film and wherein the matching circuit is formed by a meandering type ¼ wavelength parallel coupling line made of an oxide superconductive film.
In the antenna module disclosed in this publication, planar antennas arrayed on the same plane and a planar circuit type superconductive high frequency circuit are formed on the same plane. Therefore, the plane where this circuit is arranged is thought to end up becoming considerably larger. Further, when forming an array of a large number of antenna elements and trying to couple a superconductive high frequency circuit to the antenna elements, the ratio of the effective area of the entire antenna in the entire circuit on the plane becomes smaller compared with the case where the superconductive high frequency circuit is not in the same plane. Therefore, to obtain the same sensitivity, there is the problem that the area of the plane becomes relatively large.
On the other hand, the no-load Q-value of a planar circuit type superconductive high frequency circuit depends on the circuit structure and material and in particular is an important factor in the crystallinity of the oxide superconductor. It is possible to obtain an oxide superconductive film (film mainly comprised of YBa2Cu3O7-δ (δ:0 to 0.2) epitaxial film with a strong c-axis crystal orientation perpendicular to the substrate surface) suitable for formation of a high Q-value circuit, but when formed into a 3D shaped part, it is not easy to obtain such an epitaxially grown film with a continuous oxide superconductive film.
According to the present invention, there is provided an antenna coupling module comprised of a planar antenna and a substrate forming a planar superconductive high frequency circuit arranged in a perpendicular direction with respect to the element surface of the planar antenna and having the planar antenna and the superconductive high frequency circuit electromagnetically coupled. In this way, the planar antenna and the substrate forming the superconductive high frequency circuit are arranged perpendicularly and the antenna and high frequency circuit are electromagnetically coupled via a space. Therefore, it is possible to arrange antenna elements at a high density and possible to produce a compact array antenna. By making this array antenna compact, it is also possible to make the system for cooling the conductors comprised of a superconductor compact as well, so it is to cut the cost of antenna production and the operating cost.